Currently, circumstantial evidence exists to relate vitamin D deficiency to defects in muscle protein metabolism. Our studies involve the assessment of individual rates of protein synthesis and degradation in rats made vitamin D deficient through the use of specially prepared vitamin D deficient feeds. These rats will be studied in conjunction with other rats fed the identical feed but supplemented, either acutely or chronically, with vitamin D. Studies will be performed in vivo utilizing pair feeding techniques along with assessment of growth rates and food intake, determinations of muscle RNA, DNA and high energy phosphate levels and assessment of ribosomal subunit profiles. In vitro studies will utilize the techniques of hemicorpus perfusion to individually assess muscle protein synthetic and degradation rates. Abnormalities in protein synthesis, if present, will be evaluated to determine whether there is a deficiency in initiation or elongation of peptide chains. The specific metabolites of vitamin D which affects muscle protein metabolism will be determined as well.